1. Field of the Invention
The present invention relates to a memory addressing method in an image data processing apparatus such as a digital copying apparatus or the like and to an apparatus using such a method and, more particularly, to a memory accessing method for efficiently processing image data to be input and output in accordance with a plurality of kinds of arrangement orders in correspondence to each kind and to an apparatus using such a method.
2. Related Background Art
Hitherto, digital copying apparatuses using various kinds of printing and reading methods have been put into practical use. An image reading unit of the digital copying apparatus or the like outputs pixel data in accordance with the order corresponding to the reading method. Arranging methods of the pixel data which is output from the image reading unit are mainly classified into the following two kinds.
1 FIG. 3A is a diagram showing a serial scan when reading an original. Reference characters A.sub.1 to A.sub.4 denote area widths which are read by an image sensor 101 by a single scan. The image sensor 101 moves from the left side to the right side (H direction) in the diagram, so that a block of A.sub.1 can be read. Then, the image sensor or the original is moved in the direction of V by only a width (width of area which is read by the image sensor) of A.sub.1 and a block of A.sub.2 is read while again moving the image sensor from the left edge in the diagram in the H direction. By sequentially repeating the above operations, an image 301 of the original is read. In the case of reading the image 301 by using the image sensor 101, the whole image 301 is read by serially scanning the areas indicated by reference characters A.sub.1 to A.sub.k (k=4 in the diagram) in the direction indicated by an arrow H in accordance with the order. The pixel data is output in accordance with the reading order. The image data comprising the pixel data which is sent in accordance with such an order is hereinafter, referred to as a "shuttle scan data".
2 FIG. 3B is a diagram for explaining the reading operation of an image scanner 401 having a width B.sub.1. In the image reading apparatus, the image 301 is read by scanning the image scanner 401 once in the direction of an arrow V. Therefore, the image reading apparatus sequentially outputs the pixel data in accordance with the raster scanning order. The image data comprising the pixel data which is sent in accordance with such an order is hereinlater referred to as a "raster scan data".
On the other hand, the order has been also predetermined in accordance with the printing method with the pixel data to be input to a printer unit of a digital copying apparatus or the like. Raster scan data is generally input to the printer unit of, for example, the electrophotographic method. Shuttle scan data is generally input to the printer unit of the method such as a serial dot method, an ink jet method, or the like for executing the printing operation while moving a print head.
On the other hand, the image data from the image reading unit is stored into a memory in order to execute various image processes or to synchronize with the printing operation timing in the printer unit. There is a case where a memory capacity of such a memory is equal to or larger than the capacity of one page of the image data or where it is smaller than one page. In any of the above cases, the pixel data is written into the memory in accordance with the sending order, while the pixel data is output from the memory in accordance with the reading-out order.
Hitherto, an image data processing apparatus of the digital copying apparatus or the like is constructed so as to have only one kind of addressing method when the memory is accessed. That is, in the case where the sending order of the pixel data from the image reading unit is equal to the sending order of the pixel data to be output to the printer unit, the pixel data is written into the memory while sequentially incrementing the address values and is read out of the memory by substantially the same addressing method as that upon writing.
Therefore, even in the case where a printing apparatus of another printing method is connected to the conventional digital copying apparatus and an image which was read by the image reading unit is printed, if the order of the pixel data which is processed by the digital copying apparatus differs from the order of the pixel data to be input to the printing apparatus, such an operation cannot be executed. On the other hand, there is also a similar problem in the case where a reading apparatus of another reading method is connected to the conventional digital copying apparatus and is used.
In recent years, a system in which a computer is connected to a digital copying apparatus and image data which is output from the computer can be printed by the digital copying apparatus has been also put into practical use. However, if the image data which is processed by a digital copying apparatus is the shuttle scan data, since the image data which is output from a computer is ordinarily raster scan data, the computer cannot be connected to the digital copying apparatus. In addition, the digital copying apparatus which handles the shuttle scan data is not suitable for image processes by the CPU and causes a deterioration in processing efficiency.
Such a problem also similarly occurs in a printer, an image scanner, or an image data processing apparatus into/from which image data is input/output as well as the digital copying apparatus. In other words, those apparatuses lack generality because the orders of the pixel data to be input/output cannot be changed.